1. Field of the Invention
The present invention generally relates to a computer-controlled photographic camera and, more particularly, to the photographic camera having built therein an electrically erasable and programmable read only memory (E.sup.2 PROM) capable of loading data associated with functions of the photographic camera.
2. Description of the Prior Art
A variety of photographic cameras are now available on the market, which make use of a microcomputer for the control of focus adjustment and exposure control. In such photographic cameras, photographic information associated with the actual photo-taking is used to be stored in a random access memory (RAM) in the microcomputer. This photographic information once stored is lost when the microcomputer is powered off, and therefore, some information, such as, for example, the cumulative or total number of shutter releases cannot be stored.
The use of a back-up power source for the random access memory makes it possible for the particular information to be stored with no substantial fear of being lost. However, the use of the back-up power source requires a space in the camera for the installation thereof, eventually making the camera relatively bulky in size and high in manufacturing cost.
The erasable and rewriteable E.sup.2 PROM does not require the use of any back-up power source and should therefore supersede the random access memory. However, the E.sup.2 PROM being available on the market has such a problem that the reliable total operating number thereof is limited by the deterioration of the erasing and write-in operations, the reliable total operating number being less than the total shutter release number of the camera. Therefore, it is difficult to adopt the E.sup.2 PROM into the camera and to control the E.sup.2 PROM.
A camera wherein the E.sup.2 PROM is built therein is disclosed in, for example, Japanese Laid-open Patent Publication No. 60-61731, published in 1985. The camera according to this prior art publication is so designed and so constructed that photographic information including, for example, the number of exposures available for a particular film, and data descriptive of the status of a film wind-up switch can be transferred from RAM onto E.sup.2 PROM at the time of removal or replacement of a power source battery or when the power source battery is going to run down, but the information and the data once transferred can be read in RAM when a fresh battery has been loaded. However, in this prior art photographic camera, all of the data are downloaded at a time, but cannot be downloaded selectively according to the contents thereof.
Other problems associated with E.sup.2 PROM lie in that E.sup.2 FROM requires a relatively large amount of electric power to carry out the rewriting and also a relatively long processing time, for example, 10 milliseconds, to complete the rewriting. This in turn brings about the increased consumption of the electric power in the camera with increase of the number of times of rewriting being performed.